Question: Phosphoric acid conjugates phosphate ion with wich acid?
Paraphrase: What acid does Phosphoric acid conjugate phosphate ion with?
SPARQL (Wikidata):  select distinct ?sbj where { ?sbj wdt:P4147 wd:Q184782 . ?sbj wdt:P31 wd:Q55168228 } 
Answer: dihydrogenphosphate ion